Contact bumps are playing an essential role in the field of semiconductor technology for contacting semiconductor devices or chips with other substrates or carriers such as printed circuit boards.
Different techniques for forming contact bumps can be used for the connection of the pads of the semiconductor devices, chips, or substrates. An example is the so-called flip-chip technique, in which the bumps are arranged as connection elements on the chip and are optionally contacted with an additional pressure sensitive adhesive to the connecting pads of a carrier substrate. The quality of the connection established between the connection surfaces of the carrier substrate and the bumps plays an essential role in the later use of the components.
In the mechanical method, a gold wire can be used, which is shaped at its tip by the action of heat into a ball. The spherical tip of the gold wire is pressed with a suitable tool to a connection surface of the substrate, so that the ball is deformed by the force applied. Then the wire is pinched off, torn or sheared across the globe, so that a bulbous body with a wire remaining on top as bumps or contact bump remains on the substrate. The remaining on the tip of bulbous body is then flattened generally in the same or another tool. This technique is known as mechanical stud bumping and is known for example from U.S. Pat. No. 5,060,843. The connection of the material of the gold bump with metallization of the pad is performed via the pressure applied and the resulting micro-welding between the two boundary surfaces.
A disadvantage of this technique, however, is that the pads on the substrate are usually not completely covered by the bumps and therefore are not sufficiently resistant to the subsequent use of this substrate to the action of moisture or other influences.